1. Field of the Invention
The present invention relates to generating shadow image data in three-dimensional compositing environments.
2. Description of the Related Art
Many post production processes have been devised and employed over the years to enhance movie productions or video films with what is commonly referred to as “special effects”. Such image enhancement has long been provided by means of using dedicated hardware, either as a scale model to be filmed and subsequently composited in post production or, more recently, by means of effects generators such as computer apparatus configured to output rendered image components to be also subsequently composited.
Technical advances in image processing systems have enabled the generalisation of the “blue screen” technique in video environments and “green screen” technique in cinematographic environments, whereby actors or models are filmed in a studio configured with blue or green saturated surroundings in order to generate a clip of foreground image frames. An alternative clip of background image frames is subsequently generated and a compositing process allows an editor to seamlessly blend the foreground and background image frames by means of keying part of the corresponding video signals, for instance the luminance or chrominance signal.
In modern image processing systems providing real-time image data processing capability, image components within an image frame such as foreground frames of a model filmed against a blue screen or rendered three-dimensional models, all exist as hierarchical sub-structures of data processing nodes within a main structure, which defines one such final image frame. Typically, such image components are generated as polygon-based three dimensional objects to be interacted with within a three-dimensional volume, known as a compositing volume or space. An image editor using such a system can amend parameters and/or data in any of said data processing nodes to aesthetically improve any image component within an image frame and assess the effectiveness of his editing in realtime.
The concept of “post-production” is however changing, as modern video or cinematographic productions increasingly develop such image components in parallel with generating actual film footage, as opposed to once the filming has finished, in order to reduce total production lead-time and costs and generate earlier revenue for the producers. A film director is thus likely to preview the day's footage with incorporating such image components composited therein at a low resolution, to determine whether additional filming is required or not before filming the next scene. For such purposes, relatively inexpensive computers may be used as image processing systems, especially when configured with hardware-based graphics accelerators, which are well known in the art.
An important problem however hinders the development of the use of inexpensive systems as described above, as hardware graphics accelerators are typically designed to best process primitives such as polygons but, although numerous methods are known with which to generate shadows of polygon objects in three dimensional environments such as analytical shadows or pixel-based shadows, said methods do not yet allow image components within such polygons, which may be understood as textures, to cast shadows themselves.